The present invention relates to an injection device with an injection valve, a valve device for controlling the injection, and a setting element for operating the valve device. The present invention further relates to a method for injecting fluid in which a setting element is activated, a valve device is operated by the setting element, and an injection valve is opened.
A generic device and a generic method are made known, for instance, in European Patent No. 0 562 046 B1. The basic requirement on such a system is that fuel injection be carried out using the highest injection pressure possible. High injection pressure has positive effects on the performance of an engine; for instance, it reduces emissions and fuel consumption. To achieve high injection pressure, a pressure booster can be provided which converts a primary pressure, e.g., provided by a pressure accumulator, into the desired high injection pressure via hydraulic pressure intensification. By making a suitable selection of surfaces of the pressure booster to which force is applied and the counterforces of elastic materials, a suitable pressure increase can be set.
To control injection, a valve device is provided which is operated by a setting element, e.g., a solenoid valve or a piezoactuator. This valve device serves to feed the primary pressure to be intensified to the pressure booster, to perform depressurization, and to refill the pressure booster after the pressure has been increased and, consequently, injection has taken place via the injection valve.
The related art uses a 3/2 valve as the valve device. In an initial control state of the 3/2 valve, the flow of fuel between a fuel inlet and the primary side of the pressure booster is blocked. On the other hand there is a connection between the primary side of the pressure booster and the leakage system. If the setting element of the injection device is now operated, the 3/2 valve switches to a transition state in which a connection exists between the fuel inlet and the primary side of the pressure booster as well as between the primary side of the pressure booster and the leakage system. When the setting element is operated further, the second control state of the 3/2 valve is accepted, in which the connection of the primary side of the pressure booster with the leakage system is blocked, but the connection between the fuel inlet and the primary side remains open. When the pressure booster is depressurized or refilled, the 3/2 valve moves through the control states described in reverse sequence.
In the solution of the related art described, the fact that high leakage rates occur proved especially problematic. They degrade the effectiveness of the injection system. Furthermore, a 3/2 valve is only conditionally suited for high-pressure applications, especially with regard for manufacture and sealing.
A generic pressure increase is useful especially in connection with a common rail system. In common rail fuel injection, primary pressure generation and injection are decoupled. The injection pressure is generated independently of the engine speed and the injection quantity and is made available in the xe2x80x9crailxe2x80x9d (fuel line) for injection. A favorable course of injection can be fundamentally achieved in this manner, because the injection pressure and injection quantity, in particular, can be determined independently of each other for each operating point of the engine. However, the pressure in the common rail is still limited to approximately 1600 bar at this time; increasing the pressure is desired for reasons related to emissions and fuel consumption. A pressure booster in combination with a common rail system could therefore deliver especially good results. The problems mentioned above exist as a result of the use of the 3/2 valve, however, which has a detrimental effect overall on the performance of the injection system.
The injection device provided by the present invention according to claim 1 is based on the related art in that the valve device includes at least one first valve and a second valve which can be operated by the setting element via a common hydraulic coupling space. In this manner, the disadvantages are prevented, for instance, that occur with the use of a 3/2 valve made known in the related art. Since both valves can be operated by the same setting element, the equipment expenditure is not increased at this point as compared with the use of a single 3/2 valve, so that, overall, the system is improved. For instance, by suitably adjusting the elastic materials, it is possible for the valves to respond to activation by the setting element at different points in time. The hydraulic coupling space also serves to provide a power-travel transfer that may be necessary and to offset tolerances, e.g. changes in length.
Preferably, a pressure booster for boosting a primary pressure is provided, which can be operated by the valve device. High injection pressure can be achieved especially well in this manner. Since it is no longer necessary to provide a 3/2 valve, the large pressure differences that arise due to the pressure booster can be controlled while avoiding high losses due to leakage.
The setting element is preferably a piezoactuator. Piezoactuators have proven successful as electronically controllable setting elements, especially since they are compact in design and perform reliably. Moreover, the setting function can be changed by changing the parameters (voltage, pulse duration) of the control.
The primary pressure is preferably provided by a common rail. It is hereby possible to combine the advantages of a common rail system with the pressure-boosted injection device. The common rail pressure, which is currently limited to approximately 1600 bar, can be intensified; this reduces emissions and fuel consumption.
It is advantageous for the injection system to be pressure-controlled. This ensures that the injection valve actually opens only above a certain threshold pressure. This guarantees the advantages of injection using high pressure under all circumstances.
Preferably, the first valve in a first state separates the primary pressure from a low-pressure space of the pressure booster, and the first valve in a second state injects the primary pressure into the low-pressure space of the pressure booster. The first valve is thereby used as a metering valve, its opening states decisively determining the supply of the system with fuel.
It is advantageous when the second valve in a first state couples a low-pressure space of the pressure booster with a leakage system, and the second valve in a second state separates the low-pressure space of the pressure booster from the leakage system. The second valve can thereby serve as a discharge valve for the pressure valve; moreover, the pressure booster can be filled using the second valve.
It is especially advantageous when the first valve and the second valve are coordinated with each other in such a way that, by operating the setting element, the second valve can first be transferred from its first state to its second state and, as a result, the first valve can be transferred from its first state to its second state. This ensures that the opening cross-sections of the valves do not overlap. This leads to a marked reduction in the leakage rate that occurs, because the second valve is already closed when the first valve is still located in its closed first state. Additionally, it is possible to open and close the first valve numerous times (in a timed manner) while the second valve remains closed.
Preferably, a low-pressure space of the pressure booster is connected with a high-pressure space of the pressure booster via a check valve, by means of which the high-pressure space can be filled. The high-pressure space must be filled in every injection cycle so that fluid is available for high-pressure injection. A check valve prevents the high pressure from the high-pressure space of the pressure booster from reaching the low-pressure space of the pressure booster; on the other hand, the check valve makes it possible for the high-pressure space to be filled from the low-pressure space.
It can also be an advantage when a high-pressure space of the pressure booster is connected with the leakage system via a check valve. This makes it possible to completely decouple the low-pressure space and the high-pressure space of the pressure booster from each other and to refill the high-pressure space using the fluid present in the leakage system.
Preferably, a differential space of the pressure booster is connected with the leakage system via a check valve, so that the differential space is not filled. Although the check valve ensures that the leakage rate that occurs in the differential space discharges into the leakage system, it prevents the differential space from being filled, which decreases the overall volume to be filled in advantageous manner.
It can also be an advantage when, instead of the low-pressure space, the high-pressure space of the pressure booster can be relieved via the second valve. In this manner, the injection valve can be discharged more quickly than in the variant with discharge on the low-pressure side of the pressure booster. When the high-pressure space is relieved via the second valve, however, it must be taken into consideration that the valve system experiences increased stress due to the high pressure in the high-pressure space.
The fact that the first valve and/or the second valve is/are (a) 2/2 valve(s) can be useful. When this is this case, the necessary logic switching functions can be carried out, which are performed by a 3/2 valve in the related art.
Preferably, the first valve and the setting element are coordinated with each other in such a way that the first valve can be transferred continuously or in stages into different opening states with different opening cross-sections. This can be advantageous in conjunction with preinjection, for instance. By throttling in the valve seat of the first valve, very small preinjection quantities with reduced injection pressure can be achieved. To achieve this, the interplay of the first valve and the setting element is designed so that continuous cross-sectional control of the first valve or a step-wise opening of the first valve is made possible. The rapid switching time of a piezoactuator can be utilized to advantage here. Additionally, due to the cross-sectional control of the first valve, the course of injection can be formed.
The present invention is based on the generic procedure according to claim 13 in that a first valve and a second valve of the valve device are operated by the setting element using a common hydraulic coupling space. Although two valves are used as replacement for one 3/2 valve, the course of the process can be designed in a simple manner. Only one single setting element and its preferably electronic control are required to operate the first valve as well as the second valve.
A pressure booster for boosting a primary pressure is preferably operated by the valve device. In this manner, an advantageously high injection pressure can be achieved in the system.
The injection valve is preferably opened when a certain pressure is exceeded in its inlet region. A pressure-controlled system of this type is especially preferred with the advantageous use of high injection pressures, because the controlling variablexe2x80x94the pressurexe2x80x94is also the decisive parameter for the quality of injection.
Preferably, the method is further designed in such a way that, when the setting element is operated, a low-pressure space of the pressure booster is decoupled from a leakage system by the closing of the second valve, which causes the primary pressure in the low-pressure space to be decoupled by the opening of the first valve, which causes the pressure in an inlet region of the injection valve to exceed a certain pressure, so that the injection valve opens, which causes the first valve to close and, as a result, the second valve opens, so that injection is ended and the pressure booster is depressurized. As a result of this course of the process, the opening cross-sections of the two valves do not overlap, which leads to an advantageous reduction in the leakage rate. Moreover, the switching states are suitable for making a rapid pressure build-up possible as well as achieving reliable discharge of the pressure booster and the injection valve. Moreover, numerous switching operations of the first valve are possible while the second valve is closed.
Preferably, the high-pressure space of the pressure booster is filled via a check valve, by means of which it is connected with the low-pressure space. Since a sufficient fluid reservoir is present in the low-pressure space when the valve is open, it is useful to use this to fill the high-pressure space via a check valve. Conversely, the high pressure from the high-pressure space cannot cross over into the low-pressure space of the pressure booster through the check valve; it is used entirely to control the injection valve.
It can also be advantageous that the high-pressure space of the pressure booster is filled via a check valve, by means of which it is connected with the leakage system. A complete decoupling from the low-pressure space and the high-pressure space of the pressure booster is then present and, at the same time, the high-pressure space can be filled from a reservoir of sufficient size.
It can also be useful when the high-pressure space of the pressure booster is relieved via the second valve. Under certain circumstances, this can lead to a more rapid discharge, although it must be taken into consideration that the valve device must bear higher pressures.
Preferably, the first valve is transferred into different opening states continuously or in stages. In this manner, using the first valve as the metering valve, the course of injection can be formed and preinjection with a small preinjection quantity and reduced injection pressure can be achieved. This is made favorable by the rapid switching times made possible with a piezoactuator.
The present invention is based on the surprising finding that, by using two valves, an injection device, especially one having a pressure booster, can be controlled in a reliable manner. The disadvantages that occur when a 3/2 valve is used are eliminated. Moreover, a disadvantageous increase in equipment expenditure does not occur. It should be pointed out here that only one single setting element is sufficient to operate both valves.